On 08/20/2013 10:48 AM, Jason Wang wrote: > On 08/16/2013 06:02 PM, Michael S. Tsirkin wrote: >> > On Fri, Aug 16, 2013 at 01:16:30PM +0800, Jason Wang wrote: >>> >> We used to limit the max pending DMAs to prevent guest from pinning too many >>> >> pages. But this could be removed since: >>> >> >>> >> - We have the sk_wmem_alloc check in both tun/macvtap to do the same work >>> >> - This max pending check were almost useless since it was one done when there's >>> >> no new buffers coming from guest. Guest can easily exceeds the limitation. >>> >> - We've already check upend_idx != done_idx and switch to non zerocopy then. So >>> >> even if all vq->heads were used, we can still does the packet transmission. >> > We can but performance will suffer. > The check were in fact only done when no new buffers submitted from > guest. So if guest keep sending, the check won't be done. > > If we really want to do this, we should do it unconditionally. Anyway, I > will do test to see the result. There's a bug in PATCH 5/6, the check: nvq->upend_idx != nvq->done_idx makes the zerocopy always been disabled since we initialize both upend_idx and done_idx to zero. So I change it to: (nvq->upend_idx + 1) % UIO_MAXIOV != nvq->done_idx. With this change on top, I didn't see performance difference w/ and w/o this patch. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
